package com.wkh.datastructure.queue;

import java.util.Iterator;

public class ArrayQueue<E> implements Queue<E>,Iterable<E>{

    private E[] array;
    private int head;
    private int tail;

    public ArrayQueue(int capacity) {
        array = (E[]) new Object[capacity+1];
    }

    /**
     * 向队列尾插入值
     *
     * @param value 待插入值
     * @return 插入成功返回true，插入失败返回false
     */
    @Override
    public boolean offer(E value) {
        if (isFull()){
            return false;
        }
        array[tail] = value;
        tail = (tail+1)%array.length;
        return true;
    }

    /**
     * 从队列获取值，并移除
     *
     * @return 如果队列非空返回队头值，否者返回null
     */
    @Override
    public E pool() {
        if (isEmpty()){
            return null;
        }
        E value = array[head];
        head = (head+1)%array.length;
        return value;
    }

    /**
     * 从队头获取值，不移除
     *
     * @return 如果队列非空返回队头值，否则返回null
     */
    @Override
    public E peek() {
        if (isEmpty()){
            return null;
        }
        return array[head];
    }

    /**
     * 检查队列是否为空
     *
     * @return 空返回true，否则返回false
     */
    @Override
    public boolean isEmpty() {
        return head == tail;
    }

    /**
     * 检查队列是否已满
     *
     * @return 满了返回true，否则返回false
     */
    @Override
    public boolean isFull() {
        return (tail+1)%array.length == head;
    }

    /**
     * Returns an iterator over elements of type {@code T}.
     *
     * @return an Iterator.
     */
    @Override
    public Iterator<E> iterator() {
        return new Iterator<E>() {

            @Override
            public boolean hasNext() {
                return head!=tail;
            }

            @Override
            public E next() {
                E value = array[head];
                head = (head+1)%array.length;
                return value;
            }
        };
    }
}
